This invention relates generally to electrographic reproduction apparatus, and more particularly to electrographic reproduction apparatus capable of simplex or single pass duplex copying.
Electrographic reproduction apparatus typically produce copies of original information on receiver members, such as cut sheets of plain bond paper. Such information copies may be respectively formed on one side of the paper sheets (referred to as simplex copies), or on both sides of such sheets (referred to as duplex copies). In certain circumstances, such as the reproduction of multi-page documents, duplex copies are desirable. This is principally due to the fact that with duplex copies there is a reduction in the amount of paper used, and duplex copies of a multi-page document are easier to read.
Commercial reproduction apparatus capable of producing duplex copies are generally classified as "two-pass" or "single pass" apparatus. In "two-pass" reproduction apparatus, information is sequentially produced electrographically on the first sides of sheets which are thereafter collected in an intermediate tray. Such sheets are then sequentially transported back through the apparatus to have information electrographically produced on the second sides of such sheets. As a result a relatively long travel path is required for transporting sheets through the reproduction apparatus twice to produce duplex copies. Therefore, the potential for jams or other sheet handling complications is increased. Moreover, the first completed duplex copy is not available for inspection until after all first side copies are produced. Thus considerable time elapses until the first completed duplex copy is produced, and any errors in such duplex copy are not determined until after all first side copies have already been made.
In single-pass reproduction apparatus selected information is electrographically produced on opposite sides of a sheet during a single pass through such apparatus. While single-pass apparatus are successful in overcoming the noted disadvantages of two-pass electrographic reproduction apparatus, they tend to introduce, in and of themselves, other disadvantages or complications. For example, U.S. Pat. No. 3,775,102 (issued Nov. 27, 1973, in the name of Punnett) shows two separate substantially complete electrographic process assemblies for reproducing information respectively on each side of a sheet. Such duplicative assemblies require precise optical alignment, substantially increase apparatus cost, and add significant complexities which reduce reliability of the apparatus.
To eliminate duplicative process assemblies, the single pass reproduction apparatus may employ an electrically biased doner/transfer roller for simultaneously transferring imagees corresponding to information to be reproduced respectively to each side of a sheet, such as shown for example in U.S. Pat. No. 3,847,478 (issued Nov. 12, 1974, in the name of Young). However, the doner/transfer roller is of complex construction and requires accurate bias control to accomplish the simultaneous image transfers. Simplification of the transfer apparatus may be accomplished by utilizing spaced conventional transfer apparatus associated with a single electrographic process assembly, such as shown for example in U.S. Pat. No. 4,194,829 (issued Mar. 25, 1980, in the name of Cavagnaro). Such apparatus requires a complex, precisely controllable sheet handling mechanism which turns the sheet over between transfers to copy information on both sides thereof.